//===--- Enum.h - Enum implementation runtime declarations ------*- C++ -*-===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
//
// Enum implementation details declarations relevant to the ABI.
//
//===----------------------------------------------------------------------===//

#ifndef POLARPHP_ABI_ENUM_H
#define POLARPHP_ABI_ENUM_H

#include <stdlib.h>

namespace polar {

struct EnumTagCounts {
   unsigned numTags, numTagBytes;
};

inline EnumTagCounts
getEnumTagCounts(size_t size, unsigned emptyCases, unsigned payloadCases) {
   // We can use the payload area with a tag bit set somewhere outside of the
   // payload area to represent cases. See how many bytes we need to cover
   // all the empty cases.
   unsigned numTags = payloadCases;
   if (emptyCases > 0) {
      if (size >= 4)
         // Assume that one tag bit is enough if the precise calculation overflows
         // an int32.
         numTags += 1;
      else {
         unsigned bits = size * 8U;
         unsigned casesPerTagBitValue = 1U << bits;
         numTags += ((emptyCases + (casesPerTagBitValue-1U)) >> bits);
      }
   }
   unsigned numTagBytes = (numTags <=    1 ? 0 :
                           numTags <   256 ? 1 :
                           numTags < 65536 ? 2 : 4);
   return {numTags, numTagBytes};
}

} // namespace polar

#endif // POLARPHP_ABI_ENUM_H
